Carburetor having an automatic choke



Sept. 13, 1966 A. s. LUCAS ETAL CARBURETOR HAVING AN AUTOMATIC CHOKE Filed March 26 1963 E A a WNW FM/ W. a we N Z R m wr S f 7 of a A 4 W/. Z 0% m M United States Patent f 3,272,486 CARBURETOP. HAVING AN AUTOMATIC CHOKE Alvin S. Lucas, Farmington, and Charles W. Sausseie,

Southtield, Mich, assignors to Holley Carburetor Company, Warren, Mich., a corporation of Michigan Filed Mar. 26, 1963, Ser. No. 268,008 7 Claims. (Cl. 261-39) This invention relates generally to internal combustion engine carburetors, and more particularly to an improved automatic choke mechanism for such carburetors.

Automatic choke control mechanisms, such as that shown by Marsee, 2,989,293, wherein an offset or unbalanced choke plate is controlled automatically in response to engine temperature and vacuum, are well known in the art. While this type of choke mechanism has operated quite satisfactorily, each engine has its own peculiar characteristics so that the specifications and operation of this choke mechanism vary from engine to engine. Furthermore, the use of the vacuum piston shown by Marsee has frequently caused a problem in that the piston and/ or the cylinder wall eventually become contaminated, causing the piston to stick to the extent that the choke does not partially open as it must when the engine is started. For this reason, it has more recently been proposed to substitute a diaphragm that cannot stick for the piston. While this solves the sticky piston problem, it introduces another problem in some engine applications.

For example, in some engine-carburetor combinations where the piston is employed, the thermostatic coil has sufiicient tension when cold to keep the choke fully closed, even during engine cranking when manifold vacuum would otherwise be sufi'icient to partially open the choke plate but not suflicient to actuate the vacuum piston. As soon as the engine starts, manifold vacuum is sufiicient to actuate the piston and open the choke plate against the force of the still cold thermostat, until the piston passes bypass ports usually formed in the cylinder wall. After the piston passes the ports, it still applies an opening force on the choke, but the force is lesser due to the bypass. This lesser force and the airflow progressively open the choke further as the thermostat warms up, until the choke is fully open when the engine has reached normal operating temperature.

However, when a diaphragm (or a positively stopped piston such as that shown by Smitley, 2,970,825) is substituted for the piston and the thermostat is strong enough to hold the choke closed against the force of the air on the unbalanced choke plate during cranking, at which time the manifold vacuum is not sufiicient to actuate the diaphragm, then the thermostat will be too strong during the cold engine driveaway. This is because in order to prevent the possibility of rupture, the diaphragm moves to a stop, which takes it out of action once the engine is started. Since the continued choke opening force formerly provided by the piston is not provided by the diaphragm, only the force of air on the unbalanced choke plate remains, and this is not suflicient to overcome the force of the thermostat. In other words, a weaker thermostat is required for proper driveaway in the case of the diaphragm. However, if a weaker thermostat is used, it will not have enough force to hold the choke closed on cranking.

Accordingly, the main object of this invention is to provide means, when a diaphragm or a stopped piston is used, for enabling a thermostatic coil that has the proper come-off time or cold drive away characteristics to hold the choke plate closed during cranking. In other words, use of the invention makes it possible to use a diaphragm or stopped piston type choke, in applications where certain disadvantages would result.

3,272,486 Patented Sept. 13, 1966 This and other objects and advantages of the invention will become apparent when reference is made to the following specification and accompanying drawings wherein:

FIGURE 1 is an elevational view, with portions thereof cut away and in cross-section, of a carburetor embodying the invention;

FIGURES 2 and 3 are fragmentary portions of FIG- URE 1 illustrating the positions of the choke elements at various other operating conditions;

FIGURE 4 is a cross-sectional view of the diaphragm housing shown in the upper left hand portion of FIG- URE 1;

FIGURE 5 is an enlarged fragmentary portion of FIG- URE 1 illustrating a modification of the invention; and

FIGURE 6 is a graph illustrating the improvement in the operation of a choke mechanism incorporating the invention.

Referring to the drawings in greater detail, FIGURE 1 illustrates a carburetor 10 formed to provide an induction passage 12 having the usual venturi restriction 14 and a throttle valve 16 pivotably mounted downstream of the venturi, on the shaft 15, the carburetor being mounted on an engine intake manifold 18. The throttle valve is opened, against the force of a spring 20 urging it closed, in the usual manner by means of a linkage 22 connected between the throttle lever 23 and the operators foot pedal (not shown). As is customary, closing of the throttle 16 is limited by an adjustable stop 24 adapted to engage one of the steps on the fast idle cam 26, the latter being positioned by the choke mechanism 28.

The choke mechanism 28 comprises a choke plate 30 pivotally mounted on shaft 31 in the air induction passage 12 upstream of the venturi. It will be noted that the choke plate is unbalanced, as usual, to open by gravity and in response to airflow through the induction passage. The force of the air tending to open the choke plate is opposed by the thermostatic coil spring 32, which in this case is mounted on the exhaust manifold 34 and pivotally connected to the choke lever 36 by the link 38, the opposing force of the thermostat being at a maximum when the engine is cold and progressively relaxed as the engine warms up. The choke lever 36 is connected to the fast idle cam by a link 40 having one end pivotally connected to the lever 36 its other end positioned in the slot 42 formed in the fast idle cam 26. The fast idle cam 26, being pivoted at 44 and weighted at 46, is thus moved by gravity in the clockwise direction until restrained by the link 40, in other words, the choke position determines the step on the fast idle cam to which the throttle is permitted to close.

The choke lever 36 also contains an arcuate slot 48 receiving one end of a link 50 having its other end pivotally secured to the stem 52 of the vacuum diaphragm as sembly 54. The vacuum diaphragm housing 54 may be formed from a pair of stamped members 56 and 58 connected together in any suitable manner, as by rolling the flange 60, so as to secure the peripheral edge of the diaphragm 62 therebetween. The stem 52 is secured to the center of the diaphragm by the use of conventional diaphragm washers 64 and 66, and the right'hand chamber of the housing is vented to atmosphere through the ports 68. The left-hand chamber 69 of the housing contains a return spring 70 urging the diaphragm to the right, except when the engine has started and manifold vacuum is communicated to the chamber 69 through the passage 72 and conduit 74.

The above described construction is now well known in the art. The improvement contemplated by the invention is the forming of the notch 76 at the end of the arcuate slot 48 of the choke lever, and it will be seen from the following description of operation of the invention that the slot 3 76 contributes a vary important function in the operation of the choke system. It will also be noted from FIGURES 1 and that one side 78 of the slot is formed at an angle to provide a camming action so that the diaphragm link may disengage itself from the notch at the proper time.

When the engine is cold and the throttle 16, is opened so as to release the choke and fast idle cam from their FIGURE 1 positions, the theremostatic coil 32 unwinds so as to close the choke plate 30, through the link 38 and the lever 36. Since the lever 36 is rotated counterclockwise, the link 50 positions itself in the slot 78, and the spring 70 in chamber 69 of the diaphragm housing urges the diaphragm 62, the stem 52 and the link 50 to the right. This cold-engine, closed-choked condition is shown by FIGURE 2.

Thus, when cranking of the cold engine begins, the choke elements are in the FIGURE 2 position. While cranking vacuum is not sufficient to actuate the diaphragm 62, it is sufficient to apply an opening force on the unbalanced choke plate 30 that would crack it open, against the closing force of the weaker thermostat, to the extent that starting would be diflicult or impossible. However, the closed-choke angle on the side '78 of the slot is such that the link cannot move out of the slot; thus, the force of the spring 70 on the link 50 assists the thermostatic coil 32 in preventing clockwise rotation of the lever 36 keeping the choke plate in the FIGURE 2 position.

When the engine is first started, after just a few seconds of cranking, the thermostatic coil 32 is still in its cold condition and urging the choke closed. However, the increased manifold vacuum supplied to chamber 69 of the diaphragm housing is now sufficient to pull diaphragm 62 to the left against the force of the spring 70, causing the link 50 to rotate the lever 36 clockwise and initially open the choke valve 30 some predetermined amount, as shown by FIGURE 3.

Since any engine vacuum after starting is suflicient to fully acutate the diaphragm 62, spring 70 being only a return spring, the extent to which the choke is initially opened is determined by the location of the positive stop 80. In the structure shown, the stop 80 is part of the housing member 56, and its exact location may be varied to suit the requirements of the particular engine-carburetor combination. Alternatively, the housing 54 could be of a standard design having an equivalent separate abutment such as shown by Smitley, 2,970,825.

Once the engine has started and the diaphragm 62 has pulled the choke plate 30 to the FIGURE 3 position, the angle assumed by the side 7 8 of the notch 7 6 is such that the link 50 can ride out of the notch 76 upon clockwise rotation of the lever 36. In other words, when the parts have assumed the FIGURE 3 position, the link 50 can no longer restrain further choke opening, which begins to occur just as soon as the resisting force of the coil 32 is relaxed. Thus, once the engine has started, both effects of the vacuum diaphragm 62 and the link 50 are lost, and the choke position is determined by a balance between the force of air flow on the offset choke plate and the choke closing force of the thermostatic coil 32, the latter force progressively decreasing as the engine heats up to normal operating temperature.

It should be apparent from the above description that link 50 cannot assist thermostatic coil 32 in holding the choke closed during cranking if the notch 76 or something equivalent thereto were not provided.

FIGURE 5 illustrates a modification of the invention wherein the slot 48' has the same purpose and effect as the slot 48 with the notch 76 shown by FIGURES 1-3. However, slot 48' is itself positioned at the same critical angle as side 78 if the slot 48. In other words, the angle at which the side 78 of the slot'48 and the slot 48' are positioned is critical and may vary with the design of the carburetor. In any event, the angle is such that the end of the link cannot ride out of the notch 76 or up the slot 48' until the diaphragm has been fully actuated against the stop 80.

FIGURE 6 is a graph illustrating the fuel-air ratios, which is dependent mostly upon the choke plate angle, provided by a particular carburetor at various cranking temperatures, with (curve A) and without (curve B) the use of the invention. Fuel-air ratios above approximately 1.5 are generally ideal for starting, and fuel-air ratios below 1.0 will usually prevent starting. It will be noted that curve A, which represents a choke embodying the invention, provides fuel-air ratios above 1.5 at all times so as to insure good starting, particularly at the higher temperatures when the thermostatic coil is already somewhat relaxed.

While only two embodiments of the invention have been disclosed and described for purposes of illustration, it is apparent that other equivalent means could be employed to assist a necessarily weaker thermostatic coil used with a diaphragm type choke in maintaining the choke plate closed during cranking. Accordingly, no limitations are intended except as recited in the appended claims.

What we claim as our invention is:

1. In an internal combustion engine carburetor having an automatic choke including a choke plate unbalanced to open in response to airflow, thermostatic means adapted to resist opening of the choke plate when the engine is cold and vacuum responsive means for opening said choke plate a predetermined amount against the closing force of the thermostatic means upon starting of the engine, and independent means including slot means for holding said choke plate closed until the engine starts, and link means connecting said vacuum responsive means to said slot means such that said link means becomes disengaged from said slot means when said vacuum responsive means is fully actuated.

2. In an internal combustion engine carburetor having an automatic choke including a choke plate unbalanced to open in response to airflow, thermostatic means adapted to resist opening of the choke plate When the engine is cold and vacuum responsive means for opening said choke plate a predetermined amount against the closing force of the thermostatic means upon starting of the engine, and independent means including slot means associated with said vacuum responsive means for holding said choke plate closed only until the engine starts, and link means connecting said vacuum responsive means to said slot means such that said link means becomes disengaged from said slot means when said vacuum responsive means is fully actuated.

3. In an internal combustion engine carburetor having an automatic choke including a choke plate unbalanced to open in response to airflow, thermostatic means adapted to resist opening of the choke plate with a greater force when the engine is cold and with a progressively lesser force as the engine warms up and vacuum responsive means for opening said choke plate a predetermined amount against the closing force of the thermostatic means upon starting of the engine, independent means including slot means for insuring that said choke plate remains closed at any temperature until the engine starts, and link means connecting said vacuum responsive means to said slot means such that said link means becomes disengaged from said slot means when said vacuum responsive means is fully actuated.

4. An internal combustion engine carburetor, comprising an automatic choke including a choke plate unbalanced to open in response to airflow, thermostatic means adapted to resist opening of the choke plate with a greater force when the engine is cold and with a progressively lesser force as the engine warms up and vacuum responsive means for opening said choke plate a predetermined amount against the closing force of the thermostatic means upon starting of the engine, and independent means including slot means for insuring that said choke plate reins QlQSfid at any temperature until the engine starts,

and -link means connecting said vacuum responsive means to said slot means such that said link means becomes disengaged from said slot means when said vacuum responsive means is fully actuated.

5. A carburetor for an internal combustion engine, said carburetor comprising a body having an air induction passage with a venturi restriction therein, a choke valve pivotally mounted on a shaft extending across said induction passage upstream of said venturi, said choke valve being offset so as to open in response to airflow, a lever fixed in said choke shaft, said lever having an arcuate slot formed therein, a thermostatic element, means adapted to be connected to a heat source of an engine for heating said thermostatic element, a first link connected between said lever and said element, said thermostatic element urging said choke valve closed when the engine is cold, a pressure responsive device actuated by engine running vacuum but not by engine cranking vacuum, a second link pivotally connected to said vacuum responsive device and having the other end thereof positioned in said slot in said lever, said slot having a notch formed at the end thereof adjacent said pressure responsive device such that said second link is engaged in said notch when said choke is closed, the side of said notch farthest removed from said pressure responsive device being formed such that said second link can become disengaged from said notch but only when said pressure responsive device is fully actuated.

6. A carburetor for an internal combustion engine, said carburetor comprising a body having an air induction passage with a venturi restriction therein, a choke valve pivotally mounted in said induction passage upstream of said venturi, said choke valve being offset so as to open in response to airflow, a lever fixed to move with said choke valve, said lever having a slot formed therein, a thermostatic coil, means adapted to be connected to a heat source of an engine for heating said thermostatic coil, a first link connected between said lever and said coil, said thermostatic coil urging said choke valve closed when the engine is cold, a pressure responsive device actuated by engine running vacuum but not by engine cranking vacuum, a second link pivotally connected to said vacuum responsive device and having the other end thereof positioned in a portion of said slot in said lever, said slot being formed such that said second link is positioned at one end thereof when said choke is closed and prevents rotation of said lever in the choke opening direction until said pressure responsive device is fully actuated.

7. A carburetor for an internal combustion engine, said carburetor comprising a body having an air induction passage with a venturi restriction therein, a choke valve pivotally mounted in said induction passage upstream of said venturi, said choke valve being offset so as to open in response to airflow, a lever fixed to move with said choke valve, said lever having a slot formed therein, a thermostatic coil, means adapted to be connected to a heat source of an engine for heating said thermostatic coil, a first link connected between said lever and said coil, said thermostatic coil urging said choke valve closed when the engine is cold, a pressure responsive device actuated by engine running vacuum but not by engine cranking vacuum, a second link having one end pivotally connected to said vacuum responsive device and the other end positioned in said slot in said lever, said slot having a portion thereof formed such that said second link prevents rotation of said lever in the choke opening direction until said pressure responsive device is fully actuated.

References Cited by the Examiner UNITED STATES PATENTS 2,215,682 9/1940 Winkler 261-52 X 2,408,104 9/ 1946 Stanton. 2,420,917 5/1947 Sutton et a1 261-51 X 2,970,825 2/ 1961 Smitley. 2,989,293 6/1961 Marsee. 2,998,233 8/1961 Marsee.

HARRY B. THORNTON, Primary Examiner. RONALD R, WEAVER, Assistant Examiner. 

1. IN AN INTERNAL COMBUSTION ENGINE CARBURETOR HAVING AN AUTOMATIC CHOKE INCLUDING A CHOKE PLATE UNBALANCED TO OPEN IN RESPONSE TO AIRFLOW, THERMOSTATIC MEANS ADAPTED TO RESIST OPENING OF THE CHOKE PLATE WHEN THE ENGINE IS COLD AND VACUUM RESPONSIVE MEANS FOR OPENING SAID CHOKE PLATE A PREDETERMINED AMOUNT AGAINST THE CLOSING FORCE OF THE THERMOSTATIC MEANS UPON STARTING OF THE ENGINE, AND INDEPENDENT MEANS INCLUDING SLOT MEANS FOR HOLDING SAID CHOKE PLATE CLOSED UNTIL THE ENGINE STARTS, AND LINK MEANS CONNECTING SAID VACUUM RESPONSIVE MEANS TO SAID SLOT MEANS SUCH THAT SAID LINK MEANS BECOMES DISENGAGED FROM SAID SLOT MEANS WHEN SAID VACUUM RESPONSIVE MEANS IS FULLY ACTUATED. 